U.S. patent number 11,186,741 [Application Number 16/556,572] was granted by the patent office on 2021-11-30 for aqueous dispersion of multistage polymer particles.
This patent grant is currently assigned to Rohm and Haas Company. The grantee listed for this patent is Rohm and Haas Company. Invention is credited to James K. Bardman, David G. Kelly, Michael W. Leonard.
United States Patent |
11,186,741 |
Bardman , et al. |
November 30, 2021 |
Aqueous dispersion of multistage polymer particles
Abstract
The present invention relates to a composition comprising an
aqueous dispersion of multistage polymer particles comprising a
first and a second phase, wherein the first phase comprises
structural units of a carboxylic acid monomer or a salt thereof,
and a nonionic ethylenically unsaturated monomer; and wherein the
second phase comprises a first and second polymer, wherein the
first phase or the second phase first polymer or both comprise
structural units of a high T.sub.g hydrophobic monomer; and wherein
the second phase second polymer comprises at least 80 percent
structural units of styrene. The high T.sub.g hydrophobic monomer
is defined as being one or more of the following monomers:
cyclohexyl methacrylate, isobornyl methacrylate, 4-t-butyl
methacrylate, t-butylstyrene, or n-butyl methacrylate. The
multistage polymer particles are useful as opaque polymers, which
are used in pigmented coating formulations to reduce the load of
TiO.sub.2. The particles exhibit excellent collapse resistance and
unusually low dry bulk density, and do not require acrylonitrile to
achieve this desired combination of properties.
Inventors: |
Bardman; James K. (Green Lane,
PA), Kelly; David G. (Ambler, PA), Leonard; Michael
W. (Collegeville, PA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Rohm and Haas Company |
Collegeville |
PA |
US |
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Assignee: |
Rohm and Haas Company
(Collegeville, PA)
|
Family
ID: |
1000005968056 |
Appl.
No.: |
16/556,572 |
Filed: |
August 30, 2019 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20200071558 A1 |
Mar 5, 2020 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62726628 |
Sep 4, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09D
133/064 (20130101); C09D 7/70 (20180101) |
Current International
Class: |
C09D
133/06 (20060101); C09D 7/40 (20180101) |
Field of
Search: |
;523/201 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Search report from corresponding European 19195251.4 application,
dated Jan. 24, 2020. cited by applicant.
|
Primary Examiner: Bernshteyn; Michael M.
Attorney, Agent or Firm: Willis; Reid S.
Claims
The invention claimed is:
1. A composition comprising an aqueous dispersion of multistage
polymer particles comprising a first and a second phase, wherein:
a) the first phase comprises, based on the weight of the first
phase, from 25 to 60 weight percent structural units of a
carboxylic acid monomer or a salt thereof, from 40 to 75 weight
percent structural units of a nonionic ethylenically unsaturated
monomer, and up to a total of 15 weight percent structural units of
styrene and a high T.sub.g hydrophobic monomer; and wherein b) the
second phase comprises a mixture of first and second polymers,
wherein 1) the first polymer comprises, based on the weight of the
first polymer, i) from 5 to 15 weight percent structural units of a
carboxylic acid monomer or a salt thereof; ii) from 45 to 55 weight
percent structural units of styrene; and iii) from 37 to 47 weight
percent structural units of methyl methacrylate or the high T.sub.g
hydrophobic monomer or a combination thereof; and 2) the second
polymer comprises, based on the weight of the second polymer, i)
from 80 to 99.9 weight percent structural units of styrene; and ii)
from 0.1 to 0.5 weight percent structural units of a
multiethylenically unsaturated monomer; wherein the
weight-to-weight ratio of the first phase to the second phase is in
the range of from 1:9 to 1:20; and wherein the weight-to-weight
ratio of the first polymer of the second phase to the second
polymer of the second phase is in the range of from 1:3 to 1:8;
with the proviso that the first phase and the first polymer of the
second phase together comprise, based on the weight of the first
phase and the first polymer of the second phase, from 2 to 15
weight percent structural units of the high T.sub.g hydrophobic
monomer, which is one or more monomers selected from the group
consisting of cyclohexyl methacrylate, isobornyl methacrylate,
4-t-butyl methacrylate, t-butylstyrene, and n-butyl
methacrylate.
2. The composition of claim 1 wherein the weight-to-weight ratio of
the first phase to the second phase is in the range of from 1:11 to
1:18; and wherein the weight-to-weight ratio of the first polymer
of the second phase to the second polymer of the second phase is in
the range of from 1:4 to 1:7.
3. The composition of claim 2 wherein a) the first phase comprises,
based on the weight of the first phase, from 25 to 50 weight
percent of structural units of a salt of a carboxylic acid monomer,
and from 40 to 70 weight percent structural units of a nonionic
ethylenically unsaturated monomer; and from 5 to 10 weight percent
structural units of the high T.sub.g hydrophobic monomer; wherein
b) the second phase first polymer comprises, based on the weight of
the second phase first polymer, from 6 to 12 weight percent
structural units of a salt of a carboxylic acid monomer; and
wherein c) the second phase second polymer comprises, based on the
weight of the second phase second polymer, from 83 to 91 weight
percent structural units of styrene; from 8 to 12 weight percent
structural units of methyl methacrylate; from 0.5 to 4 weight
percent structural units of an alkali metal salt of methacrylic
acid of acrylic acid; and from 0.1 to 0.4 weight percent structural
units of a multiethylenically unsaturated monomer.
4. The composition of claim 2 wherein a) the first phase comprises,
based on the weight of the first phase, from 30 to 50 weight
percent of structural units of a salt of a carboxylic acid monomer,
and from 50 to 70 weight percent structural units of a nonionic
ethylenically unsaturated monomer; wherein b) the second phase
first polymer comprises, based on the weight of the second phase
first polymer, from 6 to 12 weight percent structural units of a
salt of a carboxylic acid monomer and from 5 to 15 weight percent
structural units of the high T.sub.g hydrophobic monomer; and
wherein c) the second phase second polymer comprises, based on the
weight of the second phase second polymer, from 83 to 91 weight
percent structural units of styrene; from 8 to 12 weight percent
structural units of methyl methacrylate; from 0.5 to 4 weight
percent structural units of an alkali metal salt of methacrylic
acid of acrylic acid; and from 0.1 to 0.4 weight percent structural
units of a multiethylenically unsaturated monomer.
5. The composition of claim 2 wherein a) the first phase comprises,
based on the weight of the first phase, from 25 to 50 weight
percent of structural units of a salt of a carboxylic acid monomer,
and from 40 to 70 weight percent structural units of a nonionic
ethylenically unsaturated monomer, and from 5 to 10 weight percent
structural units of the high T.sub.g hydrophobic monomer; wherein
b) the second phase first polymer comprises, based on the weight of
the second phase first polymer, from 6 to 12 weight percent
structural units of a salt of a carboxylic acid monomer and from 5
to 15 weight percent structural units of the high T.sub.g
hydrophobic monomer; wherein c) the second phase second polymer
comprises, based on the weight of the second phase second polymer,
from 83 to 91 weight percent structural units of styrene; from 8 to
12 weight percent structural units of methyl methacrylate; from 0.5
to 4 weight percent structural units of an alkali metal salt of
methacrylic acid of acrylic acid; and from 0.1 to 0.4 weight
percent structural units of a multiethylenically unsaturated
monomer.
6. The composition of claim 5 wherein a) the second phase second
polymer is a mixture of polymers comprising second phase second
polymer A and second phase second polymer B, wherein b) second
phase second polymer A comprises, based on the weight of second
phase second polymer A, from 78 to 86.5 weight percent structural
units of styrene, from 12 to 18.5 weight percent structural units
of methyl methacrylate, from 1 to 4 weight percent structural units
of methacrylic acid or acrylic acid, and from 0.1 to 0.4 weight
percent of a multiethylenically unsaturated monomer; wherein c)
second phase second polymer B comprises, based on the weight of
second phase second polymer B, at least 98 weight percent
structural units of styrene, and wherein d) the weight-to-weight
ratio of second phase second polymer A to second phase second
polymer B is in the range of from 3:1 to 6:1.
7. The composition of claim 2 wherein the second phase comprises
less than 1 weight percent structural units of acrylonitrile,
methacrylonitrile, acrylamide, and methacrylamide, based on the
weight of the second phase.
8. The composition of claim 7 wherein the second phase comprises
less than 0.1 weight percent structural units of acrylonitrile,
methacrylonitrile, acrylamide, and methacrylamide, based on the
weight of the second phase.
9. The composition of claim 1 which further comprises a rheology
modifier, a binder, TiO.sub.2, and at least one additive selected
from the groups consisting of surfactants, defoamers, biocides,
dispersants, coalescents, and neutralizing agents.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an aqueous dispersion of
multistage polymer particles that is useful for improving hiding
efficiency in a pigmented coatings formulation.
Titanium dioxide (TiO.sub.2) is the opacifying pigment of choice
for use in paint formulations due to its exceptionally high
refractive index; however, the high cost of TiO.sub.2 has motivated
researchers to investigate ways to reduce its loading while
maintaining high opacifying (hiding) efficiency. One such approach
has been the development and commercialization of high scattering
polymeric pigments known as opaque polymers, which have been found
to preserve hiding efficiency at a lower pigment volume
concentration (PVC) TiO.sub.2. U.S. Pat. No. 6,020,435 discloses
the preparation of an aqueous dispersion of core-shell polymer
particles containing acid-functionalized cores, which are converted
to opaque polymers upon neutralization of the core and subsequently
coating a substrate with the dispersion, thereby allowing water to
evaporate to form a film with voided particles.
The efficiency improvement from opaque polymers arises primarily
from two factors: Low dry bulk density and collapse resistance;
unfortunately, efforts to achieve lower dry bulk density to achieve
further improvements in hiding efficiency reduces resistance to
collapse. This correlation is unsurprising because low dry bulk
densities correlate with a larger core, therefore a larger
weight-to-weight core-to-shell ratio at the desired particle size;
the result is a thinner shell that is more susceptible to collapse.
It has been found that acrylonitrile incorporation into an
intermediate or post-intermediate polymerization stage--the stage
or stages following the core stage--results in the formation of
opaque polymers with lower dry bulk density and at an acceptable
collapse resistance; nevertheless, acrylonitrile is acutely toxic
and has been observed to cause mucous membrane irritation,
headaches, dizziness, and nausea to exposed workers. Therefore, it
would be advantageous to prepare collapse resistant low dry bulk
density polymer particles without acrylonitrile
functionalization.
SUMMARY OF THE INVENTION
The present invention addresses a need in the art by providing a
composition comprising an aqueous dispersion of multistage polymer
particles comprising a first and a second phase, wherein:
a) the first phase comprises, based on the weight of the first
phase, from 25 to 60 weight percent structural units of a
carboxylic acid monomer or a salt thereof, from 40 to 75 weight
percent structural units of a nonionic ethylenically unsaturated
monomer, and up to a total of 15 weight percent structural units of
styrene and a high T.sub.g hydrophobic monomer; and wherein
b) the second phase comprises a mixture of first and second
polymers, wherein 1) the first polymer comprises, based on the
weight of the first polymer, i) from 5 to 15 weight percent
structural units of a carboxylic acid monomer or a salt thereof;
ii) from 45 to 55 weight percent structural units of styrene; and
iii) from 37 to 47 weight percent structural units of methyl
methacrylate or the high T.sub.g hydrophobic monomer or a
combination thereof; and 2) the second polymer comprises, based on
the weight of the second polymer, i) from 80 to 99.9 weight percent
structural units of styrene; and ii) from 0.1 to 0.5 weight percent
structural units of a multiethylenically unsaturated monomer;
wherein the weight-to-weight ratio of the first phase to the second
phase is in the range of from 1:9 to 1:20; and wherein the
weight-to-weight ratio of the first polymer of the second phase to
the second polymer of the second phase is in the range of from 1:3
to 1:8;
with the proviso that the first phase and the first polymer of the
second phase together comprise, based on the weight of the first
phase and the first polymer of the second phase, from 2 to 15
weight percent structural units of the high T.sub.g hydrophobic
monomer, which is one or more monomers selected from the group
consisting of cyclohexyl methacrylate, isobornyl methacrylate,
4-t-butyl methacrylate, t-butylstyrene, and n-butyl
methacrylate.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a composition comprising an aqueous
dispersion of multistage polymer particles comprising a first and a
second phase, wherein:
a) the first phase comprises, based on the weight of the first
phase, from 25 to 60 weight percent structural units of a
carboxylic acid monomer or a salt thereof, from 40 to 75 weight
percent structural units of a nonionic ethylenically unsaturated
monomer, and up to a total of 15 weight percent structural units of
styrene and a high T.sub.g hydrophobic monomer; and wherein
b) the second phase comprises a mixture of first and second
polymers, wherein 1) the first polymer comprises, based on the
weight of the first polymer, i) from 5 to 15 weight percent
structural units of a carboxylic acid monomer or a salt thereof;
ii) from 45 to 55 weight percent structural units of styrene; and
iii) from 37 to 47 weight percent structural units of methyl
methacrylate or the high T.sub.g hydrophobic monomer or a
combination thereof; and 2) the second polymer comprises, based on
the weight of the second polymer, i) from 80 to 99.9 weight percent
structural units of styrene; and ii) from 0.1 to 0.5 weight percent
structural units of a multiethylenically unsaturated monomer;
wherein the weight-to-weight ratio of the first phase to the second
phase is in the range of from 1:9 to 1:20; and wherein the
weight-to-weight ratio of the first polymer of the second phase to
the second polymer of the second phase is in the range of from 1:3
to 1:8;
with the proviso that the first phase and the first polymer of the
second phase together comprise, based on the weight of the first
phase and the first polymer of the second phase, from 2 to 15
weight percent structural units of the high T.sub.g hydrophobic
monomer, which is one or more monomers selected from the group
consisting of cyclohexyl methacrylate, isobornyl methacrylate,
4-t-butyl methacrylate, t-butylstyrene, and n-butyl
methacrylate.
The multistage polymer particles of the present invention
preferably have a core-shell morphology wherein the first phase
corresponds to the core and the second phase corresponds to the
shell. The core may be produced by a single stage or a multistage
process, preferably in the presence of a chain transfer agent such
as n-dodecyl mercaptan or mercaptoethanol. The core may also be
prepared from a seed process. A preferred method of preparing the
core is described in U.S. Pat. No. 6,020,435.
Preferably, the first phase comprises from 30, more preferably from
35, and most preferably from 38 weight percent, to preferably 50,
more preferably to 45, and most preferably to 42 weight percent
structural units of a salt of a carboxylic acid monomer, based on
the weight of the first phase. As used herein, the term "structural
units" refers to the remnant of the recited monomer after
polymerization. For example, a structural unit of a salt of
methacrylic acid, where M.sup.+ is a counterion, preferably a
lithium, sodium, or potassium counterion, is as illustrated:
##STR00001##
The first phase also preferably comprises from 50, more preferably
from 55, and most preferably from 58 weight percent, to preferably
70, more preferably to 65, and most preferably to 62 weight percent
structural units of a nonionic ethylenically unsaturated
monomer.
The first phase preferably comprises from 5 to 10 weight percent
total structural units of styrene and/or a high T.sub.g hydrophobic
monomer selected from the group consisting of cyclohexyl
methacrylate, isobornyl methacrylate, 4-t-butyl methacrylate,
t-butylstyrene, and n-butyl methacrylate. The term "high T.sub.g
monomer" refers to a monomer that forms a homopolymer that is not
film-forming at 25.degree. C. In one preferred embodiment, the
first phase comprises from 5, more preferably from 6 weight percent
to 10 weight percent structural units of the high T.sub.g
hydrophobic monomer, based on the weight of the first phase. In
another embodiment, the first phase comprises, based on the weight
of the first phase, less than 10, more preferably less than 5, and
most preferably less than 1 weight percent structural units of
styrene.
Examples of carboxylic acid functionalized monomers include
methacrylic acid, acrylic acid, and itaconic acid, with acrylic
acid and methacrylic acid being preferred. Examples of nonionic
ethylenically unsaturated monomers include C.sub.1-C.sub.10 alkyl
acrylates and methacrylates such as methyl methacrylate, ethyl
acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate,
and 2-ethylhexyl acrylate; and styrene. Methyl methacrylate and
butyl methacrylate are preferred nonionic ethylenically unsaturated
monomers used to prepare the first phase.
The average particle size of the first phase is preferably in the
range of from 80 nm to 150 nm as measured by light scattering using
a BI-90 Plus Brookhaven Particle Analyzer.
The second phase first polymer preferably comprises from 6, more
preferably from 7 weight percent, to 12, more preferably to 9
weight percent structural units of a salt of a carboxylic acid
monomer, preferably an alkali metal salt of methacrylic acid of
acrylic acid. The second phase second polymer preferably comprises
from 83 to 91 weight percent structural units of styrene;
preferably from 8 to 12 weight percent structural units of methyl
methacrylate; preferably from 0.5 to 4 weight percent structural
units of a salt of a carboxylic acid monomer, preferably an alkali
metal salt of methacrylic acid or acrylic acid; and preferably from
0.1 to 0.4 weight percent structural units of a multiethylenically
unsaturated monomer such as divinyl benzene or allyl methacrylate.
In another embodiment, the second phase first polymer comprises
from 5 to 15 weight percent structural units of the high T.sub.g
hydrophobic monomer, based on the weight of the second phase first
polymer. In another embodiment, the second phase first polymer
comprises, based on the weight of the second phase first polymer,
less than 10, more preferably less than 5, and most preferably less
than 1 weight percent structural units of styrene.
The weight-to-weight ratio of the first phase to the second phase
is preferably in the range of from 1:11, more preferably from 1:12,
to 1:18, and more preferably to 1:16; and the weight-to-weight
ratio of the first polymer of the second phase to the second
polymer of the second phase is preferably in the range of from 1:4,
more preferably from 1:5, to preferably 1:7.
The multistage polymer particles are preferably prepared in three
stages from the aqueous dispersion of the first phase polymer
particles. In a preferred method of preparing the aqueous
dispersion of multistage polymer particles, a first monomer
emulsion (ME 1) comprising methacrylic acid, methyl methacrylate,
and styrene are contacted in a kettle with an aqueous dispersion of
first phase (core) polymer particles having a solids content in the
range of from 20, more preferably from 25, to 40, more preferably
to 35 weight percent, and copolymerized under emulsion
polymerization conditions to form a dispersion of core/tie-layer
polymer particles. In one embodiment, the core polymer particles
comprise from 5, more preferably from 6 weight percent, to 15, and
more preferably to 10 weight percent structural units of the
hydrophobic high T.sub.g monomer. ME 1 preferably comprises from 6,
more preferably from 7 weight percent, to 12, and more preferably
to 9 weight percent of methacrylic acid or acrylic acid based on
the weight of ME 1 monomers; preferably from 48 to 52 weight
percent styrene based on the weight of ME 1 monomers; and
preferably from 20 to 40 weight percent methyl methacrylate, based
on the weight of ME 1 monomers. In one embodiment, ME 1 comprises 0
weight percent of the hydrophobic high T.sub.g monomer; in another
embodiment, ME 1 comprises from 2, and more preferably from 4
weight percent, to 12, and more preferably to 10 weight percent of
the hydrophobic high T.sub.g monomer based on the weight of ME 1
monomers. The core polymer particles or the tie-layer or both
comprise structural units of a high T.sub.g hydrophobic monomer.
The weight-to-weight ratio of ME 1 to core is in preferably the
range of from 0.5:1, more preferably from 1:1, to 4:1, and more
preferably to 3:1.
The second phase second polymer may be prepared in a single stage
but is advantageously prepared in two stages (designated as ME 2
and ME 3) as follows: Upon completion of addition of ME 1 to the
kettle, a second monomer emulsion (ME 2) comprising from 78 to 86.5
weight percent styrene, from 12 to 18.5 weight percent methyl
methacrylate, from 1 to 4 weight percent methacrylic acid or
acrylic acid, and from 0.1 weight percent to 0.6 weight percent
allyl methacrylate of divinyl benzene is added to the kettle under
emulsion polymerization conditions. ME 2 also preferably includes
from 0.2 to 0.8 weight percent of linseed oil fatty acid. The
weight-to-weight ratio of ME 2 to ME 1 is preferably in the range
of from 3.5:1, more preferably from 4:1, and most preferably from
4.5:1, to 6:1, more preferably to 5.5:1, and most preferably to
5:1.
After a suitable hold period of .about.15 minutes, a third monomer
emulsion (ME 3), which contains styrene and 4-hydroxy TEMPO, is fed
into the reactor followed by addition of hot deionized water and a
neutralizing amount of a base such as NH.sub.4OH or an alkali metal
hydroxide such as concentrated NaOH. The dispersion is
advantageously chased with t-butyl hydroperoxide (t-BHP) and
isoascorbic acid (IAA) and the contents were filtered to remove any
coagulum. The weight-to-weight ratio of ME 3 to ME 2 is preferably
in the range of from 0.1:1, more preferably from 0.15:1 to 0.5:1,
more preferably to 0.3:1, and most preferably to 0.25:1.
Accordingly, in another aspect of the present invention, the second
phase second polymer is a mixture of polymers, one of which (second
phase second polymer A) comprises, based on the weight of the
second phase second polymer A, from 78 to 86.5 weight percent
structural units of styrene, from 12 to 18.5 weight percent
structural units of methyl methacrylate, from 1 to 4 weight percent
structural units of methacrylic acid or acrylic acid, and from 0.1
weight percent to 0.6 weight percent structural units of a
multiethylenically unsaturated monomer; and a second of which
(second phase second polymer B) comprises, based on the weight of
second phase second polymer B, preferably at least 98 weight
percent, preferably 100 weight percent structural units of styrene,
wherein the weight-to-weight ratio of second phase second polymer A
to second phase second polymer B is in the range of from 3:0:1,
more preferably from 3.5:1, more preferably from 4:1, and most
preferably from 4.5:1, to 6:1, more preferably to 5.5:1, and most
preferably to 5:1.
Preferably, the average particle size of the neutralized multistage
polymer particles as measured by light scattering using a BI-90
Plus Brookhaven Particle Analyzer is in the range of from 150 nm,
more preferably from 200 nm, most preferably from 350 nm; to 600
nm, more preferably to 500 nm, most preferably to 450 nm. The
solids content of the aqueous dispersion of multistage polymer
particles is preferably in the range of from 10 to 35 weight
percent.
The aqueous dispersion of multistage polymer particles is useful as
an opacifying polymeric additive that allows for the reduced
loading of TiO.sub.2 in paint formulations. When formulations
containing these opacifying polymer additives are applied as a
coating to a substrate and allowed to dry, collapse resistant
opaque polymers with a dry bulk density in the range of 0.50 to
0.55 g/cc were formed. Collapse resistant opaque polymers with dry
bulk densities at this low a level have until now only been
achieved with inclusion of acrylonitrile in the second phase;
however, it has been surprisingly discovered that acrylonitrile, as
well as methacrylonitrile, acrylamide, and methacrylamide, are no
longer necessary to achieve the properties heretofore only
achievable with the inclusion of these difficult to handle
monomers. Accordingly, the second phase of the multistage polymer
particles preferably comprises less than 10 weight percent, more
preferably less than 1 weight percent, more preferably less than
0.1 weight percent, and most preferably 0 structural units of
acrylonitrile, methacrylonitrile, acrylamide, and methacrylamide,
based on the weight of the second phase.
The aqueous dispersion of multistage polymer particles of the
present invention is useful as a supplementary opacifying pigment
in paint formulations. In another aspect, the present invention is
a pigmented water-based coatings composition comprising a
dispersion of the multistage polymer particles, a rheology
modifier, a binder, TiO.sub.2, and at least one additive selected
from the groups consisting of surfactants, defoamers, biocides,
dispersants, coalescents, and neutralizing agents.
S/Mil Measurements
Kubelka-Munk Scattering Coefficient (S/Mil)
The scattering coefficient (S/Mil) is a measure of the opacity of
the aqueous dispersion of multistage polymer particles. A sample of
the dispersion was blended with RHOPLEX.TM. AC-264 Emulsion Polymer
(AC-264, A Trademark of The Dow Chemical Company or Its Affiliates)
on a solids basis at a weight-to-weight ratio of 15% aqueous
dispersion/85% AC-264. A 7-mil wet film of the blend is drawn over
a sheet of black vinyl that was measured for thickness in four
small defined areas with an Ames Gauge. The film was dried for 2 h
at low relative humidity (<40% R.H.). The reflectance of the dry
film was measured by a Gardner Instrument Reflectometer over the
four defined areas. The thickness of the dried film was also
determined over the same defined areas using the Ames Gauge. The
Scattering coefficient was calculated for each of defined areas
as:
.times..times..times. ##EQU00001## ##EQU00001.2##
.times..times..times..times..times..times. ##EQU00001.3##
The four S/Mil measurements were then averaged to obtain the S/Mil
for the film.
Collapse
Collapse is an indication of the ability of disperse multistage
polymer particles to resist the forces of drying acting on the
walls of the internal microvoid. These forces are at their greatest
when the humidity is high, which causes the particles to dry
slowly. Collapse is determined using essentially the same procedure
that is used in determining S/Mil above except that a second
drawdown is dried overnight at 85% R.H., then dried at <40% R.H.
for 1 h.
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times. ##EQU00002##
EXAMPLES
The preparation of the aqueous dispersion of the core was carried
out as described in U.S. Pat. No. 6,020,435. Table 1 illustrates
the monomers and relative amounts used to prepare the aqueous
dispersions of the cores, as well as the solids content and average
particle size of the core particles, as measured by a Brookhaven BI
90 particle size analyzer. MMA refers to methyl methacrylate; MAA
refers to methacrylic acid; CHMA refers to cyclohexyl methacrylate;
t-BuSty refers to t-butylstyrene; Sty refers to styrene; t-BuMA
refers to t-butyl methacrylate; t-BuMA refers to t-butyl
methacrylate.
Also, the term tie-coat is used to describe the polymers formed
from monomers in ME 1.
TABLE-US-00001 TABLE 1 Monomer Distribution, Particle Size, and
Solids Content of Cores Intermediate Ex # Monomer Distribution
Particle Size % Solids 1 66 MMA/34 MAA 140 nm 32.1% 2 62 MMA/34
MAA/4 CHMA 140 nm 32.1% 3 58 MMA/34 MAA/8 CHMA 138 nm 32.1% 4 56
MMA/34 MAA/10 t-BuSty 141 nm 32.4% 5 56 MMA/10 Sty/34 MAA 135 nm
31.9% 6 56 MMA/10 t-BuMA/34 MAA 140 nm 31.6% 7 55 MMA/10 BMA/35 MAA
140 nm 31.7% 8 56 MMA/8 IBOMA/34 MAA 140 nm 31.7%
Comparative Example 1--Preparation of Aqueous Dispersion of Polymer
Particles with No Hydrophobic High T.sub.g Monomer in Core or ME
1
Deionized water (800 g) was added to a 5-L 4-necked round bottom
flask (kettle) equipped with a paddle stirrer, thermometer,
nitrogen inlet, and reflux condenser; the kettle was heated to
89.degree. C. under N.sub.2 at which time sodium persulfate (3.2 g)
dissolved deionized water (30 g) was added, followed immediately
the addition the core of Intermediate Example 1 (186.9 g). A
monomer emulsion (ME 1), which was prepared by mixing deionized
water (60.0 g), sodium dodecyl sulfate (SDS, 4.0 g, 23% active),
styrene (60.0 g), MMA (50.4 g), and MAA (9.6 g) was added to the
kettle at a rate of 3.0 g/min at a temperature of 77-79.degree. C.
Upon completion of ME 1 addition, a second monomer emulsion (ME 2),
which was prepared by mixing deionized water (187.0 g), SDS (8.0 g,
23% active), styrene (491.4 g), MMA (72.0 g), MAA (10.8 g), linseed
oil fatty acid (LOFA 3.6 g), and allyl methacrylate (ALMA 1.80 g),
was fed to the reactor at a rate of 10 g/m for 15 min during which
time the temperature was allowed to rise to 84.degree. C. After 15
min, the feed rate of ME 2 was increased to 20 g/min and a separate
mixture of sodium persulfate (0.75 g) dissolved in deionized water
(62.0 g) was co-fed to the reactor at a rate of 1.5 g/min. The
temperature of the reaction mixture was allowed to increase to
92-93.degree. C. during the course of the ME 2 feed. Upon
completion of addition of ME 2 and the co-feed, a mixture of 0.1%
FeSO4.7H.sub.2O (20.0 g)/1% VERSENE.TM. Chelating Agent (2.0 g, A
Trademark of The Dow Chemical Company or its Affiliates) was added
to the kettle; the temperature was held for 15 min at
.about.92.degree. C., after which time a third monomer emulsion (ME
3), which was prepared by mixing deionized water (46 g), SDS (1.7
g), styrene (144.0 g), and
4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl(4-hydroxy TEMPO, 3.0
g), was fed to the kettle at a rate of 40 g/min. After completion
of ME 3 addition, hot deionized water (300 g) was added to the
kettle followed by addition of a mixture of 50% sodium hydroxide
(26.6 g) and hot water (450 g) over 10 min. The reaction mixture
was then held for 5 min at a temperature of 80-85.degree. C., after
which time a mixture of t-BHP (1.2 g) and deionized water (25 g)
was added to the kettle. A mixture of isoascorbic acid (IAA, 0.65
g) and deionized water (50 g) was then fed to the kettle over 25
min. Upon completion of the IAA co-feed, the kettle was cooled to
room temperature and the contents filtered to remove any coagulum
formed. The final latex had a solids content of 28.5%, a pH of 8.6,
and a particle size of 427 nm. The dry density of this polymer was
calculated to be 0.517 g/mL. Low RH S/Mil was 1.34, High RH S/Mil
was 0.97, and % Collapse was 28%.
Example 1--Preparation of Aqueous Dispersion of Polymer Particles
with CHMA in ME 1
The procedure of Comparative Example 1 was carried out except that
Intermediate Example 1 core (188.1 g) was used; and ME 1 monomers
were styrene (60.0 g), MMA (44.4 g), MAA (9.6 g), and CHMA (6.0 g).
The final latex had a solids content of 28.5%, a pH of 8.9, and a
particle size of 384 nm. The dry density of this polymer was
calculated to be 0.533 g/cc. Low RH S/Mil was 1.31, High RH S/Mil
was 1.23, and % Collapse was 6%.
Example 2--Preparation of Aqueous Dispersion of Polymer Particles
with CHMA in ME 1
The procedure of Comparative Example 1 was followed except that
Intermediate Example 1 core (188.7 g) was used; and ME 1 monomers
were styrene (60.0 g), MMA (26.4 g), MAA (9.6 g), and CHMA (24.0
g). The final latex had a solids content of 28.8%, a pH of 8.9, and
a particle size of 415 nm. The dry density of this polymer was
calculated to be 0.541 g/cc. Low RH S/Mil was 1.28, High RH S/Mil
was 1.22, and % Collapse was 5%.
Example 3--Preparation of Aqueous Dispersion of Polymer Particles
with CHMA in the Core
The procedure of Comparative Example 1 was carried out except that
Intermediate Example 3 core (186.9 g) was used; and ME 1 monomers
were styrene (60.0 g), MMA (26.4 g), MAA (9.6 g), and CHMA (12.0
g). The final latex had a solids content of 28.2%, a pH of 8.9, and
a particle size of 412 nm. The dry density of this polymer was
calculated to be 0.541 g/cc. Low RH S/Mil was 1.32, High RH S/Mil
was 1.32, and % Collapse was 0%.
Example 4--Preparation of Aqueous Dispersion of Polymer Particles
with t-Butyl Styrene in the Core
The procedure of Comparative Example 1 was followed except that the
core (185.2 g) was made as described in Intermediate Example 4. The
final latex had a solids content of 28.4%, a pH of 8.75, and a
particle size of 409 nm. The dry density of this polymer was
calculated to be 0.541 g/cc. Low RH S/Mil was 1.40, High RH S/Mil
was 1.28, and % Collapse was 8.5%.
Example 5--Preparation of Aqueous Dispersion of Polymer Particles
with t-Butyl Styrene in the Core and Tiecoat
The procedure of Comparative Example 1 was carried except that
Intermediate Example 4 core (185.2 g) was used; and ME 1 monomers
were styrene (60.0 g), MMA (44.4 g), MAA (9.6 g), t-BuSty (6.4 g).
The final latex had a solids content of 28.4%, a pH of 8.85, and a
particle size of 403 nm. The dry density of this polymer was
calculated to be 0.543 g/cc. Low RH S/Mil was 1.40, High RH S/Mil
was 1.33, and % Collapse was 5%.
Comparative Example 2--Preparation of Aqueous Dispersion of Polymer
Particles with Styrene in the Core
The procedure of Comparative Example 1 was followed except that the
core (188.1 g) was made as described in Intermediate Example 5. The
final latex had a solids content of 28.5%, a pH of 8.7, and a
particle size of 403 nm. The dry density of this polymer was
calculated to be 0.539 g/cc. Low RH S/Mil was 1.40, High RH S/Mil
was 1.19, and % Collapse was 15.0%.
Example 6--Preparation of Aqueous Dispersion of Polymer Particles
with Styrene in the Core and CHMA in Tie-Coat
The procedure of Comparative Example 1 was carried out except that
Intermediate Example 5 core (186.3 g) was use; and ME 1 monomers
were styrene (60.0 g), MMA (38.4. g), MAA (9.6 g), and CHMA (12.0
g). The final latex had a solids content of 28.4%, a pH of 8.5, and
a particle size of 405 nm. The dry density of this polymer was
calculated to be 0.536 g/cc. Low RH S/Mil was 1.38, High RH S/Mil
was 1.33, and % Collapse was 3.5%.
Example 7--Preparation of Aqueous Dispersion of Polymer Particles
with t-Butyl Methacrylate in the Core and the Tie-Coat
The procedure of Comparative Example 1 was carried out except that
Intermediate Example 6 core (189.9 g) was used; and ME 1 monomers
were styrene (60.0 g), MMA (38.4. g), MAA (9.6 g), and t-BuMA (12.0
g). The final latex had a solids content of 28.6%, a pH of 8.5, and
a particle size of 437 nm. The dry density of this polymer was
calculated to be 0.543 g/cc. Low RH S/Mil was 1.35, High RH S/Mil
was 1.25, and % Collapse was 7.5%.
Example 8--Preparation of Aqueous Dispersion of Polymer Particles
with t-Butyl Methacrylate in the Core and Cyclohexyl Methacrylate
in the Tie-Coat
The procedure of Comparative Example 1 was carried out except that
Intermediate Example 6 core (189.9 g) was used; and ME 1 monomers
were styrene (60.0 g), MMA (44.4. g), MAA (9.6 g), and CHMA (6.0
g). The final latex had a solids content of 28.6%, a pH of 8.4, and
a particle size of 424 nm. The dry density of this polymer was
calculated to be 0.531 g/cc. Low RH S/Mil was 1.40, High RH S/Mil
was 1.31, and % Collapse was 6.5%.
Example 9--Preparation of Aqueous Dispersion of Polymer Particles
with t-Butyl Methacrylate in the Core and Tie-Coat
The procedure of Comparative Example 1 was carried out except that
Intermediate Example 7 core (189.3 g) was used; and ME 1 monomers
were styrene (60.0 g), MMA (38.4. g), MAA (9.6 g), and t-BMA (12.0
g). The final latex had a solids content of 28.8%, a pH of 8.5, and
a particle size of 427 nm. The dry density of this polymer was
calculated to be 0.569 g/cc. Low RH S/Mil was 1.29, High RH S/Mil
was 1.22, and % Collapse was 5.5%.
Example 10--Preparation of Aqueous Dispersion of Polymer Particles
with Isobornyl Methacrylate in the Core
The procedure of Comparative Example 1 was carried out except that
the core (186.3 g) was made as described in Intermediate Example 8.
The final latex had a solids content of 28.5%, a pH of 8.8, and a
particle size of 424 nm. The dry density of this polymer was
calculated to be 0.540 g/cc. Low RH S/Mil was 1.31, High RH S/Mil
was 1.21 and % Collapse was 7.5%.
Example 11--Preparation of Aqueous Dispersion of Polymer Particles
with Isobornyl Methacrylate in the Tie-Coat
The procedure of Comparative Example 1 was carried out except that
Intermediate Example 1 core (188.7 g) was used; and ME 1 monomers
were styrene (60.0 g), MMA (38.4. g), MAA (9.6 g), and IBOMA (12.0
g). The final latex had a solids content of 28.6%, a pH of 8.9, and
a particle size of 413 nm. The dry density of this polymer was
calculated to be 0.539 g/cc. Low RH S/Mil was 1.27, High RH S/Mil
was 1.23, and % Collapse was 3.0%.
The data demonstrate that dispersions of multistage polymer
particles having a dry bulk density of less than 0.55 g/cc can be
prepared with a collapse resistance of less than 10%, which is
considered acceptable in the field of opaque polymers.
* * * * *